README.android
author Sam Lantinga <slouken@libsdl.org>
Sat, 16 Feb 2013 04:40:32 -0800
changeset 6892 bb72759b42a2
parent 6816 b3d3ef1e15b5
child 6962 6ce8edb5577b
permissions -rw-r--r--
Switched package name back, at the request of Manuel A. Fernandez Montecelo
     1 ================================================================================
     2 Simple DirectMedia Layer for Android
     3 ================================================================================
     4 
     5 Requirements:
     6 
     7 Android SDK
     8 http://developer.android.com/sdk/index.html
     9 
    10 Android NDK r4 or later
    11 http://developer.android.com/sdk/ndk/index.html
    12 
    13 
    14 ================================================================================
    15  How the port works
    16 ================================================================================
    17 
    18 - Android applications are Java-based, optionally with parts written in C
    19 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
    20 the SDL library
    21 - This means that your application C code must be placed inside an android 
    22 Java project, along with some C support code that communicates with Java
    23 - This eventually produces a standard Android .apk package
    24 
    25 The Android Java code implements an "activity" and can be found in:
    26 android-project/src/org/libsdl/app/SDLActivity.java
    27 
    28 The Java code loads your game code, the SDL shared library, and
    29 dispatches to native functions implemented in the SDL library:
    30 src/SDL_android.cpp
    31 
    32 Your project must include some glue code that starts your main() routine:
    33 src/main/android/SDL_android_main.cpp
    34 
    35 
    36 ================================================================================
    37  Building an app
    38 ================================================================================
    39 
    40 Instructions:
    41 1. Copy the android-project directory wherever you want to keep your projects
    42    and rename it to the name of your project.
    43 2. Move or symlink this SDL directory into the <project>/jni directory
    44 3. Edit <project>/jni/src/Android.mk to include your source files
    45 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
    46 
    47 If you want to use the Eclipse IDE, skip to the Eclipse section below.
    48 
    49 5. Edit <project>/local.properties to point to the Android SDK directory
    50 6. Run 'ant debug' in android/project. This compiles the .java and eventually 
    51    creates a .apk with the native code embedded
    52 7. 'ant debug install' will push the apk to the device or emulator (if connected)
    53 
    54 Here's an explanation of the files in the Android project, so you can customize them:
    55 
    56 android-project/
    57 	AndroidManifest.xml	- package manifest. Among others, it contains the class name
    58 				  of the main activity.
    59 	build.properties	- empty
    60 	build.xml		- build description file, used by ant. The actual application name
    61 				  is specified here.
    62 	default.properties	- holds the target ABI for the application, can range between
    63 				  android-5 and android-16
    64 	local.properties	- holds the SDK path, you should change this to the path to your SDK
    65 	jni/			- directory holding native code
    66 	jni/Android.mk		- Android makefile that can call recursively the Android.mk files
    67 				  in all subdirectories
    68 	jni/SDL/		- (symlink to) directory holding the SDL library files
    69 	jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
    70 	jni/src/		- directory holding your C/C++ source
    71 	jni/src/Android.mk	- Android makefile that you should customize to include your 
    72                                   source code and any library references
    73 	res/			- directory holding resources for your application
    74 	res/drawable-*		- directories holding icons for different phone hardware. Could be
    75 				  one dir called "drawable".
    76 	res/layout/main.xml	- Usually contains a file main.xml, which declares the screen layout.
    77 				  We don't need it because we use the SDL video output.
    78 	res/values/strings.xml	- strings used in your application, including the application name
    79 				  shown on the phone.
    80 	src/org/libsdl/app/SDLActivity.java - the Java class handling the initialization and binding
    81 				  to SDL.  Be very careful changing this, as the SDL library relies
    82 				  on this implementation.
    83 
    84 
    85 ================================================================================
    86  Customizing your application name
    87 ================================================================================
    88 
    89 To customize your application name, edit AndroidManifest.xml and replace
    90 "org.libsdl.app" with an identifier for your product package.
    91 
    92 Then create a Java class extending SDLActivity and place it in a directory
    93 under src matching your package, e.g.
    94 	src/com/gamemaker/game/MyGame.java
    95 
    96 Here's an example of a minimal class file:
    97 --- MyGame.java --------------------------
    98 package com.gamemaker.game;
    99 
   100 import org.libsdl.app.SDLActivity; 
   101 
   102 /* 
   103  * A sample wrapper class that just calls SDLActivity 
   104  */ 
   105 
   106 public class MyGame extends SDLActivity { }
   107 
   108 ------------------------------------------
   109 
   110 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   111 class, .e.g. "MyGame"
   112 
   113 ================================================================================
   114  Customizing your application icon
   115 ================================================================================
   116 
   117 Conceptually changing your icon is just replacing the icon.png files in the
   118 drawable directories under the res directory. There are 3 directories for
   119 different screen sizes. These can be replaced with 1 dir called 'drawable',
   120 containing an icon file 'icon.png' with dimensions 48x48 or 72x72.
   121 
   122 You may need to change the name of your icon in AndroidManifest.xml to match
   123 this icon filename.
   124 
   125 ================================================================================
   126  Loading assets
   127 ================================================================================
   128 
   129 Any files you put in the "assets" directory of your android-project directory
   130 will get bundled into the application package and you can load them using the
   131 standard functions in SDL_rwops.h.
   132 
   133 There are also a few Android specific functions that allow you to get other
   134 useful paths for saving and loading data:
   135 SDL_AndroidGetInternalStoragePath()
   136 SDL_AndroidGetExternalStorageState()
   137 SDL_AndroidGetExternalStoragePath()
   138 
   139 See SDL_system.h for more details on these functions.
   140 
   141 The asset packaging system will, by default, compress certain file extensions.
   142 SDL includes two asset file access mechanisms, the preferred one is the so
   143 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
   144 GC, but given this method does not work on compressed assets, there is also the
   145 "Input Stream" method, which is automatically used as a fall back by SDL. You
   146 may want to keep this fact in mind when building your APK, specially when large
   147 files are involved.
   148 For more information on which extensions get compressed by default and how to
   149 disable this behaviour, see for example:
   150     
   151 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
   152 
   153 ================================================================================
   154  Pause / Resume behaviour
   155 ================================================================================
   156 
   157 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
   158 the event loop will block itself when the app is paused (ie, when the user
   159 returns to the main Android dashboard). Blocking is better in terms of battery
   160 use, and it allows your app to spring back to life instantaneously after resume
   161 (versus polling for a resume message).
   162 
   163 Upon resume, SDL will attempt to restore the GL context automatically.
   164 In modern devices (Android 3.0 and up) this will most likely succeed and your
   165 app can continue to operate as it was.
   166 
   167 However, there's a chance (on older hardware, or on systems under heavy load),
   168 where the GL context can not be restored. In that case you have to listen for
   169 a specific message, (which is not yet implemented!) and restore your textures
   170 manually or quit the app (which is actually the kind of behaviour you'll see
   171 under iOS, if the OS can not restore your GL context it will just kill your app)
   172 
   173 ================================================================================
   174  Threads and the JAVA VM
   175 ================================================================================
   176 
   177 For a quick tour on how Linux native threads interoperate with the JAVA VM, take
   178 a look here: http://developer.android.com/guide/practices/jni.html
   179 If you want to use threads in your SDL app, it's strongly recommended that you
   180 do so by creating them using SDL functions. This way, the required attach/detach
   181 handling is managed by SDL automagically. If you have threads created by other
   182 means and they make calls to SDL functions, make sure that you call
   183 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   184 your thread automatically anyway (when you make an SDL call), but it'll never
   185 detach it.
   186 
   187 ================================================================================
   188  Using STL
   189 ================================================================================
   190 
   191 You can use STL in your project by creating an Application.mk file in the jni
   192 folder and adding the following line:
   193 APP_STL := stlport_static
   194 
   195 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   196 
   197 ================================================================================
   198  Additional documentation
   199 ================================================================================
   200 
   201 The documentation in the NDK docs directory is very helpful in understanding the
   202 build process and how to work with native code on the Android platform.
   203 
   204 The best place to start is with docs/OVERVIEW.TXT
   205 
   206 
   207 ================================================================================
   208  Using Eclipse
   209 ================================================================================
   210 
   211 First make sure that you've installed Eclipse and the Android extensions as described here:
   212 	http://developer.android.com/sdk/eclipse-adt.html
   213 
   214 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   215  * File -> New -> Other
   216  * Select the Android -> Android Project wizard and click Next
   217  * Enter the name you'd like your project to have
   218  * Select "Create project from existing source" and browse for your project directory
   219  * Make sure the Build Target is set to Android 2.0
   220  * Click Finish
   221 
   222 
   223 ================================================================================
   224  Using the emulator
   225 ================================================================================
   226 
   227 There are some good tips and tricks for getting the most out of the
   228 emulator here: http://developer.android.com/tools/devices/emulator.html
   229 
   230 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   231 
   232 Notice that this software emulator is incredibly slow and needs a lot of disk space.
   233 Using a real device works better.
   234 
   235 ================================================================================
   236  Troubleshooting
   237 ================================================================================
   238 
   239 You can create and run an emulator from the Eclipse IDE:
   240  * Window -> Android SDK and AVD Manager
   241 
   242 You can see if adb can see any devices with the following command:
   243 	adb devices
   244 
   245 You can see the output of log messages on the default device with:
   246 	adb logcat
   247 
   248 You can push files to the device with:
   249 	adb push local_file remote_path_and_file
   250 
   251 You can push files to the SD Card at /sdcard, for example:
   252 	adb push moose.dat /sdcard/moose.dat
   253 
   254 You can see the files on the SD card with a shell command:
   255 	adb shell ls /sdcard/
   256 
   257 You can start a command shell on the default device with:
   258 	adb shell
   259 
   260 You can remove the library files of your project (and not the SDL lib files) with:
   261 	ndk-build clean
   262 
   263 You can do a build with the following command:
   264 	ndk-build
   265 
   266 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   267 	ndk-build V=1
   268 
   269 If your application crashes in native code, you can use addr2line to convert the
   270 addresses in the stack trace to lines in your code.
   271 
   272 For example, if your crash looks like this:
   273 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   274 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   275 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   276 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   277 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   278 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   279 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   280 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   281 I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   282 
   283 You can see that there's a crash in the C library being called from the main code.
   284 I run addr2line with the debug version of my code:
   285 	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   286 and then paste in the number after "pc" in the call stack, from the line that I care about:
   287 000014bc
   288 
   289 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   290 
   291 You can add logging to your code to help show what's happening:
   292 
   293 #include <android/log.h>
   294 
   295 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   296 
   297 If you need to build without optimization turned on, you can create a file called
   298 "Application.mk" in the jni directory, with the following line in it:
   299 APP_OPTIM := debug
   300 
   301 
   302 ================================================================================
   303  Memory debugging
   304 ================================================================================
   305 
   306 The best (and slowest) way to debug memory issues on Android is valgrind.
   307 Valgrind has support for Android out of the box, just grab code using:
   308 	svn co svn://svn.valgrind.org/valgrind/trunk valgrind
   309 ... and follow the instructions in the file README.android to build it.
   310 
   311 One thing I needed to do on Mac OS X was change the path to the toolchain,
   312 and add ranlib to the environment variables:
   313 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
   314 
   315 Once valgrind is built, you can create a wrapper script to launch your
   316 application with it, changing org.libsdl.app to your package identifier:
   317 --- start_valgrind_app -------------------
   318 #!/system/bin/sh
   319 export TMPDIR=/data/data/org.libsdl.app
   320 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   321 ------------------------------------------
   322 
   323 Then push it to the device:
   324 	adb push start_valgrind_app /data/local
   325 
   326 and make it executable:
   327 	adb shell chmod 755 /data/local/start_valgrind_app
   328 
   329 and tell Android to use the script to launch your application:
   330 	adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
   331 
   332 If the setprop command says "could not set property", it's likely that
   333 your package name is too long and you should make it shorter by changing
   334 AndroidManifest.xml and the path to your class file in android-project/src
   335 
   336 You can then launch your application normally and waaaaaaaiiittt for it.
   337 You can monitor the startup process with the logcat command above, and
   338 when it's done (or even while it's running) you can grab the valgrind
   339 output file:
   340 	adb pull /sdcard/valgrind.log
   341 
   342 When you're done instrumenting with valgrind, you can disable the wrapper:
   343 	adb shell setprop wrap.org.libsdl.app ""
   344 
   345 
   346 ================================================================================
   347  Known issues
   348 ================================================================================
   349 
   350 - TODO. I'm sure there's a bunch more stuff I haven't thought of